1//===- InlineAlways.cpp - Code to inline always_inline functions ----------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements a custom inliner that handles only functions that
11// are marked as "always inline".
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/Transforms/IPO.h"
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/Analysis/AliasAnalysis.h"
18#include "llvm/Analysis/AssumptionCache.h"
19#include "llvm/Analysis/CallGraph.h"
20#include "llvm/Analysis/InlineCost.h"
21#include "llvm/IR/CallSite.h"
22#include "llvm/IR/CallingConv.h"
23#include "llvm/IR/DataLayout.h"
24#include "llvm/IR/Instructions.h"
25#include "llvm/IR/IntrinsicInst.h"
26#include "llvm/IR/Module.h"
27#include "llvm/IR/Type.h"
28#include "llvm/Transforms/IPO/InlinerPass.h"
29
30using namespace llvm;
31
32#define DEBUG_TYPE "inline"
33
34namespace {
35
36/// \brief Inliner pass which only handles "always inline" functions.
37class AlwaysInliner : public Inliner {
38  InlineCostAnalysis *ICA;
39
40public:
41  // Use extremely low threshold.
42  AlwaysInliner() : Inliner(ID, -2000000000, /*InsertLifetime*/ true),
43                    ICA(nullptr) {
44    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
45  }
46
47  AlwaysInliner(bool InsertLifetime)
48      : Inliner(ID, -2000000000, InsertLifetime), ICA(nullptr) {
49    initializeAlwaysInlinerPass(*PassRegistry::getPassRegistry());
50  }
51
52  static char ID; // Pass identification, replacement for typeid
53
54  InlineCost getInlineCost(CallSite CS) override;
55
56  void getAnalysisUsage(AnalysisUsage &AU) const override;
57  bool runOnSCC(CallGraphSCC &SCC) override;
58
59  using llvm::Pass::doFinalization;
60  bool doFinalization(CallGraph &CG) override {
61    return removeDeadFunctions(CG, /*AlwaysInlineOnly=*/ true);
62  }
63};
64
65}
66
67char AlwaysInliner::ID = 0;
68INITIALIZE_PASS_BEGIN(AlwaysInliner, "always-inline",
69                "Inliner for always_inline functions", false, false)
70INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
71INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
72INITIALIZE_PASS_DEPENDENCY(CallGraphWrapperPass)
73INITIALIZE_PASS_DEPENDENCY(InlineCostAnalysis)
74INITIALIZE_PASS_END(AlwaysInliner, "always-inline",
75                "Inliner for always_inline functions", false, false)
76
77Pass *llvm::createAlwaysInlinerPass() { return new AlwaysInliner(); }
78
79Pass *llvm::createAlwaysInlinerPass(bool InsertLifetime) {
80  return new AlwaysInliner(InsertLifetime);
81}
82
83/// \brief Get the inline cost for the always-inliner.
84///
85/// The always inliner *only* handles functions which are marked with the
86/// attribute to force inlining. As such, it is dramatically simpler and avoids
87/// using the powerful (but expensive) inline cost analysis. Instead it uses
88/// a very simple and boring direct walk of the instructions looking for
89/// impossible-to-inline constructs.
90///
91/// Note, it would be possible to go to some lengths to cache the information
92/// computed here, but as we only expect to do this for relatively few and
93/// small functions which have the explicit attribute to force inlining, it is
94/// likely not worth it in practice.
95InlineCost AlwaysInliner::getInlineCost(CallSite CS) {
96  Function *Callee = CS.getCalledFunction();
97
98  // Only inline direct calls to functions with always-inline attributes
99  // that are viable for inlining. FIXME: We shouldn't even get here for
100  // declarations.
101  if (Callee && !Callee->isDeclaration() &&
102      CS.hasFnAttr(Attribute::AlwaysInline) &&
103      ICA->isInlineViable(*Callee))
104    return InlineCost::getAlways();
105
106  return InlineCost::getNever();
107}
108
109bool AlwaysInliner::runOnSCC(CallGraphSCC &SCC) {
110  ICA = &getAnalysis<InlineCostAnalysis>();
111  return Inliner::runOnSCC(SCC);
112}
113
114void AlwaysInliner::getAnalysisUsage(AnalysisUsage &AU) const {
115  AU.addRequired<InlineCostAnalysis>();
116  Inliner::getAnalysisUsage(AU);
117}
118